[MrNatural]

Here is my question: how long did they originally think shuttles would serve for - what was their "retirement" date?..

Ivan, the shuttle's airframe was originally certified for 100 flights; however, the
shuttles were intended to fly much more often. The Columbia was therefore like
an automobile that had only been driven 20K miles but was 30 years old.

There's a reason why car makers say five years or 50,000 miles,

[Petronski]

The Columbia was therefore like an automobile that had only been driven 20K miles but was 30 years old.

There was also a refurbishment/refit in 1991, as I have read on this thread. I would love to have such a car.